import cv2
import numpy as np

img = img1 = cv2.imread(r"/\images\008.jpg")

def change(x):
    global img
    bgr = cv2.getTrackbarPos("BGR", "test")
    if bgr == 0:
        img = img1
    else:
        img = img1[:,:,bgr - 1]
cv2.namedWindow("test")
cv2.createTrackbar("BGR", "test", 0, 3, change)

while True:
    cv2.imshow("test", img)
    key = cv2.waitKey(50000)
    if key == 27:
        break
cv2.destroyAllWindows()